Computer modelling, steady state and pre-state kinetic studies on the interaction of actin, myosin subfragment-one and ATP were carried out in a continuing effort to elucidate the steps which occur when actin activates the myosin ATPase. Our results strongly suggest that myosin subfragment-one can hydrolyze ATP both when it is free in solution or bound to actin. Hence, there is no mandatory dissociation step in the actomyosin ATPase cycle.